High contrast front projection display panel and a method of making a high contrast front projection display panel

ABSTRACT

An optical display panel which provides improved viewing contrast for front projection applications, and a method of producing a stacked optical waveguide panel for front projection applications, are disclosed. The optical panel includes a plurality of stacked optical waveguides, wherein each waveguide has a back face and an outlet face at opposing ends of each waveguide, and wherein each waveguide is formed of a core between an opposing pair of cladding layers, and at least one reflector connected to the back face of at least one waveguide, wherein the at least one reflector receives image light incident through at least one waveguide from the outlet face, and wherein the at least one reflector redirects the image light back through the at least one waveguide out of the outlet face. In the preferred embodiment, the outlet face is rendered black by inclusion of black within or between cladding layers. The method includes stacking a plurality of clear strips of plastic, placing a double sided, dark colored adhesive between each strip of plastic, pressing the stack, forming, at two opposite ends of the stack, a back face and an outlet face, and connecting at least one reflector to the back face.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] Not applicable.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention is directed generally to a planar opticaldisplay, and, more particularly, to a high contrast front projectiondisplay panel and a method of making a high contrast front projectiondisplay panel.

[0004] 2. Description of the Background

[0005] Video display screens typically use cathode ray tubes (CRTs) forprojecting an image onto the outlet face of the screen. A typical screenof this type has a width to height ratio of 4:3 with 525 vertical linesof resolution. An electron beam must be scanned both horizontally andvertically on the screen to form a number of pixels, which collectivelyform the image. Conventional cathode ray tubes have a practical limit insize and are relatively deep to accommodate the required electron gun.Larger screen televisions are available which typically include variousforms of image projection for increasing the screen image size. However,such screens may experience limited viewing angle, limited resolution,decreased brightness, and decreased contrast, particularly in displayscreens using front projections. This is, in part, due to the use ofwhite screens to allow the screen to reflect the front projection backto the user. Thus, because the screen is white, the darkest black levelthat can be displayed is “screen white”, the color of the screen whenthe projection is off, due to the fact that black light cannot beprojected. Consequently, the projection must be either on, or off, toproduce white, or black, respectively. Thus, where black is viewed on afront screen projection system, the viewer is actually seeing the whiteof the background, i.e the absence of projected light, which the humaneye sees as black in the context of the white light projected elsewhereon the background, meaning that the presence of the optical spectrumprojected onto the white background forms a “whiter than white” color,which the eye sees as white. This is the reason that a room must bedarkened in order for a viewer to see black on a front projectionscreen.

[0006] Optical panels can be created using a plurality of stackedwaveguides, and may be rendered black using at least one black claddinglayer between transparent cores of the waveguides. The cladding layersdisclosed therein have a lower index of refraction than the waveguidecores for effectuating substantial internal reflection of the imagelight channeled through the cores, and thereby improve contrast, i.e.thereby improve the appearance of black images on a screen. Such opticalpanel displays have typically been operated in a rear projection mode.

[0007] Therefore, the need exists for a display panel that allows forfront projection, while also providing the appearance of a black screento improve viewing contrast and to eliminate the need to dim lights inorder to allow a viewer to see black images.

BRIEF SUMMARY OF THE INVENTION

[0008] The present invention is directed to an optical display panelwhich provides improved viewing contrast for front projectionapplications. The optical panel includes a plurality of stacked opticalwaveguides, wherein each waveguide has a back face and an outlet face atopposing ends of each waveguide, and wherein each waveguide is formed ofa core between an opposing pair of cladding layers, and at least onereflector connected to the back face of at least one waveguide, whereinthe at least one reflector receives image light incident through atleast one waveguide from the outlet face, and wherein the at least onereflector redirects the image light back through the at least onewaveguide out of the outlet face. In the preferred embodiment, theoutlet face is rendered black by inclusion of black within or betweencladding layers.

[0009] The present invention is also directed to a method of producing astacked optical waveguide panel for front projection applications. Inone preferred embodiment of the present invention, clear strips ofplastic, which are preferably approximately {fraction (3/4)}″ by 40″,and approximately {fraction (20/1000)}″ thick, are stacked, with a thindouble sided black adhesive strip between each plastic strip. The stackmay include 2000-3000 of the strips. The strip stack is then pressedunder high pressure to eliminate air bubbles and improve adhesion.Another method includes coating a plurality of glass sheets on each oftwo faces with a first substance having an index of refraction lowerthan that of the glass sheets, placing a first coated glass sheet into atrough sized slightly larger than the first coated glass sheet, fillingthe trough with a thermally curing black epoxy, stacking the pluralityof coated glass sheets within the filled trough, curing the epoxy,forming, at two opposite ends of the stack, a back face and an outletface, and connecting at least one reflector to the back face.

[0010] The optical display panel for front projection applicationssolves problems experienced in the prior art by providing a displaypanel that allows for front projection, while also providing theappearance of a black screen to improve viewing contrast and toeliminate the need to dim lights in order to allow a viewer to see blackimages.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0011] For the present invention to be clearly understood and readilypracticed, the present invention will be described in conjunction withthe following figures, wherein:

[0012]FIG. 1 is an isometric view illustrating a cross section of a highcontrast front projection display panel;

[0013]FIG. 2 illustrates the use of a high contrast front projectiondisplay panel for movie projection;

[0014]FIG. 3A is a cross sectional view of a high contrast frontprojection display panel having a planar diffusor and planar reflectiveportion;

[0015]FIG. 3B is a cross sectional view of a high contrast frontprojection display panel having a planar diffusor and an angledreflective portion;

[0016]FIG. 3C illustrates the reflection of light in a high contrastfront projection display panel;

[0017]FIG. 3D is a cross sectional view of a high contrast frontprojection display panel having a diffusive reflector;

[0018]FIG. 3E is a cross sectional view of a high contrast frontprojection display panel having an embossed diffusive reflector; and

[0019]FIG. 4 is an isometric view illustrating a plurality of stackedwaveguides.

DETAILED DESCRIPTION OF THE INVENTION

[0020] It is to be understood that the figures and descriptions of thepresent invention have been simplified to illustrate elements that arerelevant for a clear understanding of the present invention, whileeliminating, for purposes of clarity, many other elements found in atypical optical display panel. Those of ordinary skill in the art willrecognize that other elements are desirable and/or required in order toimplement the present invention. However, because such elements are wellknown in the art, and because they do not facilitate a betterunderstanding of the present invention, a discussion of such elements isnot provided herein.

[0021]FIG. 1 is an isometric view schematic illustrating a display panel10. The display panel 10 may include a plurality of stacked opticalwaveguides 16 a, an outlet face 16 at one end of a body 18 formed by theplurality of stacked waveguides 16 a, a back face 12 at a second end ofthe body 18, at least one reflector 19 that reflects light within thebody 18 at the back face 12, and a light generator 21.

[0022] The body 18 is preferably solid and receives light 14 along thesurface of the outlet face 16. The light 14 is passed through the body18 after entering the outlet face 16, and is reflected back through thebody 18 from the at least one reflector 19 to the outlet face 16. In apreferred embodiment of the present invention, the body 18 is formed ofthe length, height, and width of the plurality of stacked waveguides 16a.

[0023] The plurality of stacked waveguides 16 a forms the body 18 of thepanel 10, forms at one end of the stack 16 a the back face 12, and at asecond end the outlet face 16. The waveguides 16 a may be formed of anymaterial known in the art to be suitable for passing electromagneticwaves therethrough, such as, but not limited to, plastics, or glass. Thepreferred embodiment of the present invention is implemented usingindividual glass or plastic or polymer sheets, which are typicallyapproximately 0.010-0.020″ thick, and which may be of a manageablelength and width. The polymer used may be a suitable plastic laminate,such as Lexan®, which is commercially available from the GeneralElectric Company®, or any polymers or acrylics, such as Plexiglass.

[0024] The waveguides 16 a are in the form of sheets or ribbonsextending the full width of the outlet face 16 and are stacked tocollectively form at their upper ends the height of the outlet face 16.The waveguides 16 a are disposed along their longitudinal lighttransmitting axes. The number of waveguides 16 a may be selected forproviding a corresponding vertical resolution of the outlet face 16. Forexample, 525 of the waveguides 16 a may be stacked to produce 525 linesof vertical resolution in the outlet face 16. Since the waveguides 16 aextend the full width of the outlet face 16, horizontal resolution maybe controlled by horizontal modulation of the image light 14.

[0025] Each of the plurality of waveguides includes a central core 26for channeling the image light 14 through the waveguides, and each core26 is disposed between cladding layers 28. In a preferred embodiment ofthe present invention, the cladding layers 28 extend completely from theback face 12 to the outlet face 16 along the entire width of the outletface 16. A black layer 30 may be disposed within or between adjoiningcladding layers 28 for absorbing ambient light 32 at the outlet face 16,and may form multi-layer cladding layers 28. The term black is usedherein to encompass not only pure black color, but additionally, anyfunctionally comparable dark color suitable for use in the presentinvention, such as dark blue. The black layer 30 is only necessarywithin the viewable region of the outlet face, but, in a preferredembodiment of the present invention, the black layer 30 extendscompletely from the back face 12 to the outlet face 16 along the entirewidth of the outlet face 16. Additionally, the cladding layers 28 may beformed of gradients.

[0026] Each central core 26 has a first index of refraction. Thecladding layers 28 have a second index of refraction, lower than that ofthe central core 26, for ensuring total internal reflection of the imagelight 14 as it travels from the outlet face 16 to the back face 12, andback to the outlet face 16. The core is thus bi-directional. In apreferred embodiment of the present invention, the cladding layers 28are transparent in order to effectuate total internal reflection of theimage light 14, and thereby maximize the brightness of the light 14 atthe outlet face 16. The black layers 30, if separate from the claddinglayers, may have any index of refraction.

[0027] The back face 12 and outlet face 16 are formed by the pluralityof waveguides 16 a, wherein one end of each waveguide 16 a forms a backface for that waveguide, and wherein the opposite end of each waveguide16 a forms an outlet for that waveguide 16 a. Each waveguide 16 aextends horizontally, and the plurality of stacked waveguides 16 aextends vertically. The light 14 may be displayed on the outlet face ina form such as, but not limited to, a video image 14 a. Consequently, ina preferred embodiment the plurality of waveguides 16 a are stackedapproximately parallel to the horizontal, thus placing the outlet face16 and the back face 12 in the same plane from the horizontal andapproximately equidistant from the horizontal.

[0028] The outlet face 16 is formed by the plurality of stacked opticalwaveguides 16 a. The outlet face 16 is at one end of the body 18, andreceives light 14 from the light generator 21. In the preferredembodiment, this light 14 is incident to the outlet face 16 at thecritical angle or lower of the waveguide 16 a, thus allowing for totalinternal reflection of the light within the waveguide 16 a, therebyallowing for approximately all light projected from the light generator21 to reach the back face 12. The outlet face 16 is defined as the frontof the body 18. Additionally, the panel 10 has a height from the top tothe bottom of the outlet face 16, and a width from the left to the rightof the outlet face 16. The width and height may be selected to producewidth to height aspect ratios of 4:3 or 16:9, for example, for use in atypical television application.

[0029] The light generator 21 generates light 14 and passes the light tooutlet face 16. The light generator 21 may be a white light projector,such as an overhead projector, or may include a light source, and/or alight modulator, and/or imaging optics, such as a video or movieprojector. The light 14 may be initially generated, for example, by thelight source. The light source may be, for example, a brightincandescent bulb, a laser, an arc lamp, an LED, an RF excited gasdischarge lamp, any solid state light source, or any phosphorescent,luminescent, or incandescent light source. The light 14 from the sourcemay then be modulated by the modulator for defining individual pictureelements, known in the art as pixels. Alternatively, the light maydefine a simple lighted item, such as an on/off switch. The imagingoptics may include light folding mirrors or lenses. The imaging opticsmay be optically aligned between the outlet face 16 and the lightmodulator for compressing or expanding and focusing the light 14 asrequired to fit the outlet face 16. The light 14, after entry into theoutlet face 16, travels through the panel body 18 to the back face 12,and reaches the at least one reflector 19. The light 14 is projected atthe waveguide critical angle or lower over the outlet face 16, and isthus directed generally horizontally upon reflection from the at leastone reflector 19 for projection outwardly from the outlet face 16.

[0030] The at least one reflector 19 is connected to at least one of theback faces 12, or is embossed into at least one of the back faces 12, inorder to redirect the light 14, which is incident in a directiongenerally horizontally inward through the body 18 from the outlet face16, back to a direction generally horizontally outward from the outletface 16. The at least one reflector may be within, pressed into, orwithout, the body 18 at the back face 12. The at least one reflector maybe connected to the back face 12 by an optical connection, being placeddirectly adjacent to the back face, or being glued to the back face,with or without air gaps, for example. The reflective portion of thereflector 19 may be, but is not limited to, a mirrored surface, such asa retro-reflector, a total internal reflection (TIR) retro-reflector, areflective serration, a reflective coating, such as a reflective tape, alens or series of lenses, a micro-lens or series of micro-lenses, aplane mirror, or a prism. Only light entering each waveguide 16 a at thecritical angle or lower reaches the back face reflector 19, as mostambient and other light will enter the waveguide 16 a at an anglegreater than the critical angle, and will consequently be absorbed bythe cladding between the waveguides 16 a, rather than being reflectedfrom the outlet face 16 to the back face 19. Therefore, ambient andother light not entering the waveguide at the critical angle or lowerwill not be reflected by the at least one reflector 19 back to theoutlet face 16, and light entering at the critical angle or lower willbe so reflected. The at least one reflector may be a reflector 19 placedat the back face 12 of each waveguide 16 a, when covered with the atleast one reflector 19, causes reflection to occur back through thewaveguide 16 a and out the outlet face 16, or the at least one reflector19 may cover several or all waveguide back faces 12 which constitute thebody 18.

[0031] Additionally, in a preferred embodiment, the at least onereflector includes a diffuser or disperser to reflect incoming light outof the outlet face 16 at, for example, 30 degrees from the vertical axisand 120 degrees from the horizontal axis. This dispersion allows forviewing by a much larger number of viewers, as those viewers can be offangle and, through the dispersion of the image light, still view theimage. For example, as shown in FIG. 2, a movie projector may project amovie onto the outlet face 16, which movie is then reflected back outthe outlet face 16, at a dispersed angle, to a wide viewing audience.

[0032] The diffuser 19 a may be attached to the reflective portion 19 bof the reflector 19, between the reflective portion 19 b and the atleast one back face 12, as shown in FIG. 3A. The diffuser 19 a may beplanar in nature, as may be the reflective portion 19 b, as shown inFIG. 3A, or the reflective portion 19 b may be angled, and may be aretroreflector, such as a TIR or mirrored surface, with a planardiffuser 19 a between that angled reflective portion 19 b and the atleast one back end, as shown in FIG. 3B. In the embodiments of FIGS. 3Aand 3B, horizontal spreading is preferably completely dependent on thediffuser 19 a, while vertical spreading is dependent on the diffuser 19a and the waveguide absorption angle, as shown in FIG. 3C. The verticaland horizontal dispersion angles should thus be tailored to the audiencelocation, and the diffuser angle of diffusion should be chosenaccordingly.

[0033] In an additional preferred embodiment shown in FIG. 3D, thereflector 19 is a diffusive mirror, which combines the reflectiveportion 19 b and the diffusor 19 a into a single element. The diffusivemirror may be a glass mirror or a plastic mirror, and includes thereflective portion 19 b on the diffusive mirror at a plane farthest fromthe at least one back face 12. A diffusive microstructure is preferablypresent on the glass or plastic under the reflective portion 19 a of thereflector 19. FIG. 3E illustrates the reflector 19 as an embossedreflective and/or diffusive microstructure, which is embossed directlyonto the at least one back face 12.

[0034] The plurality of stacked waveguides 16 a, including the at leastone reflector, may be formed by several methods. The plurality ofstacked waveguides is shown in FIG. 4. A plurality of glass sheets maybe used as the central cores 26, and may be individually coated with, ordipped within, a clear, or black, substance having an index ofrefraction lower than that of the glass, such as, but not limited to,polyurethane, clear coat containing dyes, silicones, cyanoacreylates,low index refraction epoxys, plastics, and polymers, thereby forming acoated glass sheet. This clear or black substance is the opposedcladding layers 28. Where a clear cladding layer is placed, a firstcoated glass sheet may then be placed in a trough sized slightly largerthan the first coated glass sheet. The trough may then be filled with athermally curing black epoxy. The black epoxy need not possess theproperties of a suitable cladding layer.

[0035] After filling of the trough with either clear sheets in a blackepoxy, or black coated sheets in any epoxy, the coated glass sheets arerepeatedly stacked, and a layer of epoxy forms between each coated glasssheet. The stacking is preferably repeated until between approximately500 and 800 sheets have been stacked. Uniform pressure may then beapplied to the stack, thereby causing the epoxy to flow to a generallyuniform level between coated glass sheets. The stack may then be bakedto cure at 80 degrees Celsius for such time as is necessary to cure theepoxy, and the stack is then allowed to cool slowly in order to preventcracking of the glass.

[0036] The back face 12 and the outlet face 16 may be cut as planar orcurved as desired, and the back face 12 may be specially shaped to forma desired shaped surface to allow for proper operation of the at leastone reflector 19. The cut portions of the panel 10 may then be polishedwith a diamond polisher to remove any saw marks. The at least onereflector 19 is then added to the back face, either in the form of acoating placed on the back face or faces 12, a mirror, lens, or prismglued to the back face or faces 12, or a reflective attachment, such asa reflective tape, being fastened to the back face or faces 12.

[0037] In an additional preferred embodiment, clear strips of plastic,which are preferably approximately {fraction (3/4)}″ by 40″, andapproximately {fraction (20/1000)}″ thick, are stacked, with a thindouble sided black adhesive strip between each plastic strip. The stackmay include 2000-3000 of the strips. The strip stack is then pressedunder high pressure to remove air bubbles and increase adhesion. In oneembodiment, the adhesive is Research AR8350, {fraction (1/1000)}″ to{fraction (2/1000)}″ thick black double sided adhesive. The adhesive maybe shades other than black, such as dark blue, and preferably rolls outlike a form of tape, in a plastic/adhesive/plastic/adhesive format. Thepressure applied to the completed stack is preferably in excess of 1,000pounds.

[0038] In a second embodiment of the present invention, the coated glasssheets or plastic strips may be coated with a black substance, such asspray paint, before being stacked with an adhesive, which need not be adark shade in this embodiment, between the strips, or before beingplaced into the epoxy trough. In another embodiment of the presentinvention, the coated blackened glass sheets may be individuallyfastened using glue or epoxy. In another embodiment of the presentinvention, both the clear substance and the black layer could be formedof a suitable substance and placed, in turn, on the glass core usingsputtering techniques known in the art, or deposition techniques knownin the art.

[0039] Those of ordinary skill in the art will recognize that manymodifications and variations of the present invention may beimplemented. The foregoing description and the following claims areintended to cover all such modifications and variations.

What is claimed is:
 1. An optical panel comprising: a plurality ofstacked optical waveguides, wherein each waveguide has a back face andan outlet face at opposing ends of each waveguide, and wherein eachwaveguide is formed of a core in contact with at least one claddinglayer; and at least one reflector connected to the back face of at leastone waveguide, wherein said at least one reflector receives image lightincident through at least one waveguide from the outlet face, andwherein said at least one reflector redirects the image light backthrough the at least one waveguide out of the outlet face.
 2. Theoptical panel of claim 1, wherein said reflector comprises a reflectiveportion and at least one diffuser.
 3. The optical panel of claim 2,wherein said diffuser causes the image light from the outlet face toexit the outlet face up to about 30 degrees from a vertical axis of theoutlet face and up to about 120 degrees from a horizontal axis of theoutlet face.
 4. The optical panel of claim 2, wherein said diffuser isattached to said reflective portion of said reflector, between saidreflective portion and the back face.
 5. The optical panel of claim 4,wherein said diffuser is planar.
 6. The optical panel of claim 5,wherein said reflective portion is planar.
 7. The optical panel of claim5, wherein said reflective portion includes at least one angled portion.8. The optical panel of claim 2, wherein said reflector is a diffusivemirror.
 9. The optical panel of claim 8, wherein the diffusive mirror isa glass mirror.
 10. The optical panel of claim 8, wherein the diffusivemirror is a plastic mirror.
 11. The optical panel of claim 9 or 10,wherein said diffuser comprises a diffusive microstructure between saidreflective portion and the back face.
 12. The optical panel of claim 12,wherein said reflector is embossed onto the back face.
 13. The opticalpanel of claim 1, wherein the image light is displayed through theoutlet face as an image.
 14. The optical panel of claim 1, wherein eachof said cladding layers extends from the back face to the outlet face.15. The optical panel of claim 1, wherein each of said cladding layersincludes at least one darkened layer.
 16. The optical panel of claim 1,further comprising a light generator which generates the light.
 17. Theoptical panel of claim 16, wherein said light generator includes a lightsource.
 18. The optical panel of claim 17, wherein said light generatorfurther includes a light modulator; and imaging optics.
 19. The opticalpanel of claim 17, wherein said light source is chosen from the groupconsisting of a laser, an arc lamp, an RF excited gas discharge lamp, asolid state light source, a phosphorescent light source, a luminescentlight source, and an incandescent light source.
 20. The optical panel ofclaim 17, wherein the image light from said light source is modulated bysaid light modulator to define pixels.
 21. The optical panel of claim20, wherein horizontal resolution at the outlet face is controlled bymodulation of the image light from said light source.
 22. The opticalpanel of claim 17, wherein said imaging optics include at least onemirror and at least one lens.
 23. The optical panel of claim 17, whereinsaid imaging optics are optically aligned between the outlet face andsaid light modulator for compressing, expanding, and focusing the lightto fit the outlet face.
 24. The optical panel of claim 1, wherein the atleast one cladding layer is disposed to absorb ambient light.
 25. Theoptical panel of claim 1, wherein each of said waveguides isbi-directional.
 26. The optical panel of claim 1, wherein said core hasa first index of refraction and wherein said cladding layer has a secondindex of refraction which is lower than the first index of refraction.27. The optical panel of claim 1, wherein each of said cores is aplastic sheet.
 28. The optical panel of claim 1, wherein said at leastone reflector is connected within the stack.
 29. The optical panel ofclaim 1, wherein said at least one reflector is connected outside thestack.
 30. The optical panel of claim 1, wherein one reflector isconnected to the back face of each waveguide.
 31. The optical panel ofclaim 1, wherein said at least one reflector comprises a retroreflector.
 32. The optical panel of claim 1, wherein said at least onereflector comprises a TIR retro reflector.
 33. The optical panel ofclaim 1, wherein said at least one reflector comprises at least oneselected from the group consisting of a reflective serration, a planemirror, and a frosted diffusive mirror.
 34. The optical panel of claim1, wherein said at least one reflector comprises a reflective tape. 35.The optical panel of claim 1, wherein said at least one reflectorcomprises curved mirror.
 36. The optical panel of claim 1, wherein saidat least one reflector comprises a reflective prism.
 37. A method ofproducing a stacked optical waveguide panel, comprising: coating aplurality of glass sheets on each of two faces with a first substancehaving an index of refraction lower than that of the glass sheets;placing a first coated glass sheet into a trough sized slightly largerthan the first coated glass sheet; filling the trough with a thermallycuring epoxy; stacking the plurality of coated glass sheets within thefilled trough; curing the epoxy; forming, at two opposite ends of thestack, a back face and an outlet face; and connecting at least onereflector to the back face.
 38. The method of claim 37, wherein saidstacking is repeated until between approximately 500 and approximately800 glass sheets are stacked.
 39. The method of claim 37, furthercomprising applying uniform pressure to the stack to produce asubstantially uniform level of epoxy between adjoining cladding layers.40. The method of claim 37, wherein said curing comprises baking at 80degrees Celsius.
 41. The method of claim 37, further comprisingpolishing the sawed stack with a diamond polisher.
 42. The method ofclaim 37, wherein said connecting comprises connecting within the stack.43. The method of claim 37, wherein said connecting comprises connectingoutside the stack.
 44. A method of forming an optical waveguide panel,comprising stacking a plurality of clear strips of plastic; placing adouble sided, dark colored adhesive between each strip of plastic;pressing the stack; forming, at two opposite ends of the stack, a backface and an outlet face; and connecting at least one reflector to theback face.
 45. The method of claim 44, wherein said connecting comprisesembossing.
 46. The method of claim 44, wherein the adhesive is about{fraction (1/1000)}″ to {fraction (2/1000)}″ thick.
 47. The method ofclaim 44, wherein said pressing comprises pressing the stack with apressure of at least 1,000 pounds.
 48. The method of claim 44, whereinthe plastic strips are about {fraction (3/4)}″ by 40″, and approximately{fraction (20/1000)}″ thick, in dimension.
 49. The method of claim 44,wherein the stack includes about 2000 to about 3000 of the plasticstrips.